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Max Arctic Sea Ice Coverage Ties All-Time Low

Each month the National Snow and Ice Data Center (NSIDC) offers an update of how much sea ice is covering the vast Arctic Ocean. This monthly comparison of how conditions are different than what satellites have observed in previous years has been a "smoking gun" that Arctic sea ice has been shrinking in recent decades (abundant other indicators show a rapidly changing Arctic). Take February 2011 for example; since the late 1970s — when satellite records began — the amount of Arctic sea ice each February has been on a steady decline, but this year it tied the record low.

The 2011 maximum Arctic sea ice coverage was 5.65 million square miles, and was tied with 2006 for the lowest on record. Credit: NSIDC.

There are two other times of the year where measurements give a good sense of how the Arctic has changed in the past 30 years. The most newsworthy time of year is when sea ice coverage hits its absolute minimum, which usually occurs sometime in September, after the long summer season of melting and before ice starts to grow up again. In recent decades, the minimum sea ice extent has been shrinking dramatically. In 2010, it was the third-lowest that had ever been recorded.

While the annual minimum sea ice coverage is always newsworthy, the point of annual maximum ice extent — which of course happens at the end of winter, right before the ice begins to melt in the spring — is perhaps more representative of the impacts of a warming Arctic.

It won’t come as a surprise to many that when we passed the day of maximum sea ice coverage this year — which NSIDC says happened on March 7 — there wasn’t as much ice to be found as in previous years. In fact, it appears 2011 has tied 2006 as the year with the smallest amount of sea ice at the point of maximum coverage, at 5.65 million square miles. The low sea ice coverage this year is consistent with the warm winter across much of the Arctic.

But the fact that there was less ice in the Arctic this winter isn’t just a sign that the season was a bit warmer than usual. It also indicates that, from year to year, there are fewer days when conditions are conducive to ice formation.

“When there isn’t as much ice in the Arctic in the summer, then the area is warms up,” explains NSIDC’s Walt Meier, who is part of the group that tracks Arctic ice coverage throughout the year. Meier says that as the sea ice melts, the ocean absorbs more of the heat, warming up the water and also the air above. These warmer temperatures last longer into the fall than they would have if there had been more summer ice, he says, which delays the time when ice starts to grow again. “In a way, it’s starting from behind and then it doesn’t have time to catch up.”

And also keep in mind that if during one summer there is below average sea ice coverage in the Arctic, then through the following winter, there would have to be more ice forming than usual, just to get back to where it started the year before.

March 7 marked the 2011 maximum Arctic sea ice extent, which tied for the lowest on record with 2006. Credit: NSIDC.

So this year’s low sea ice extent is probably a combination of a few factors. Firstly, at the end of the 2010 melt season last September, the extent of ice in the Arctic was the third-lowest on record, which means there wasn’t nearly as much ice left to build on as in previous years. On top of that, last year’s low ice extent meant there was more heat in the Arctic, and this delayed the start of ice formation in the fall. Finally, this past winter, parts of the Arctic experienced unusually mild conditions, which did not help matters much.

Now that we’re on our way into this year’s melt season, the fact that the ice coverage is already starting off at a record low level could foreshadow what we might see in the Arctic over the next six months. But Meier says a low winter ice extent doesn’t necessarily mean that summer is going to see dramatic melting.

“There doesn’t seem to be a lot of correlation between a low winter and a low summer,” he says. “A lot is going to depend on what happens over the spring and summer. The air and water temperatures, and the wind, over the central Arctic are going to be the most important in determining how much ice melts.”